What happens when you have a problem with a product or service you purchased that requires multiple separate departments in a company (in some cases, whole separate companies and subcontractors) to work together to solve, but the company structure is such that no department ever actually talks directly to any other department about anything (or even has any means of doing so), and no department is ever allowed to do something on behalf of another.

You'll be bounced endlessly back and forth between a string of ostensibly cheerful, helpful people, with long hold times between each and every one, getting a different person whenever you're sent back to a department you already spoke to, and every single time you have to explain the entire problem all over again from scratch, plus everything that every previous department has told you up to that point. Never actually solves any problem; this hellish sequence invariably ends when someone hangs up on you by accident when they actually meant to transfer you yet again, whereupon you have to start over from square one.

Zen are the worst ISP ever; they had me doing the call centre conga for weeks.